Re: [boost] Report from Berlin C++ Standards Committee meeting

From: Steve Hutton (shutton_at_[hidden])
Date: 2006-04-15 04:37:00

On 2006-04-14, Darren Cook <darren_at_[hidden]> wrote:
>> Just a quick note that the SOCI database library has been progressing
>> nicely.  The current release supports Oracle and Postgresql, and we
>> have just recieved contributions of backends for SQLite and MySQL.
>> The next release (later this month) should thus contain support for
>> these 4 databases.
>> 
>> http://soci.sourceforge.net/
>
> I just had a look and as others have said this is looking good. The
> design criteria all seem reasonable. I'd suggest getting into the boost
> review queue sooner rather than later.

Thanks! We should have the 2.1 release out around the end of the month,
and after that I think we can create a TODO list for boostification and
get into the review queue.
>
> The biggest thing that concerned me was having to define the size of a
> vector to limit the amount of data that is read, e.g.
>
>    std::vector<int> valsOut(100);
>    sql << "select val from numbers", into(valsOut);

The idea is that you want to tune the batch size for best performance.
I'm open to considering other ways of specifying the batch size...

> What if I simply want to get all data, in one batch. Or, more likely, if
> I forget to specify a size does it give an error or simply return no data:
>    std::vector<int> valsOut;
>    sql << "select val from numbers", into(valsOut);

This will throw an exception.  

> Also if, in the first example, more than 100 records were available, is
> there a flag set somewhere to tell me that I didn't get all the data? Or
> does the vector size of 100 add a "LIMIT 100" to the SQL query so there
> is no way to tell?

The idea is that to select all rows, you fetch within a loop.  The
vector gets resized to contain the number of rows returned.

const int BATCH_SIZE = 30;
std::vector<int> valsOut(BATCH_SIZE);
Statement st = (sql.prepare <<  "select value from numbers", 
                                into(valsOut));
st.execute();
while (st.fetch())
{
    std::vector<int>::iterator pos;
    for(; pos != valsOut.end(); ++pos)
    {
        cout << *pos << '\n'; 
    }
}

http://soci.sourceforge.net/doc/statements.html

Steve